He returned to civilian life in 1918, and resumed his studies at the University of Aberdeen later that year, graduating in 1920 with a degree in Pure Science, with special distinction in Geology.
Some of his most important work concerned the Scottish Coalfields and their associated rocks, in Ayrshire, Dumfriesshire, Dumbartonshire, Lanarkshire and Midlothian, leading to significant upward revisions to reserves estimates.
He was elected a Fellow of the Society in 1932 his proposers being John Smith Flett, Murray Macgregor, James Ernest Richey and Robert Campbell.
[3] Two obituaries capture the character of the man nicely: "Johnnie Simpson was a man of exceptional kindliness, generosity and charm, loved by all of his friends ... [his professional] reputation was the result of a patient and selfless devotion to research worthy of the high traditions of Scottish natural science";[4] and "To be his companion on a Highland traverse was ... both an inspiration and memory to treasure.
He possessed other qualities - an innate courtesy, forbearance, helpfulness and loyalty - which gained for him the affection of many friends and for which he will long be remembered ... the end came as he himself might surely have wished it to come.